1. Field of the Invention
The present invention relates to a method for producing a resist composition used in finer processing in a process for producing a semiconductor apparatus including a semiconductor device, particularly a composition for a resist film used in multilayer resist method.
2. Description of the Related Art
Amid LSI's technological development of higher integration and higher speed, fine patterning with a smaller dimension of a circuit pattern has rapidly been developed. Accordingly, lithography technology has achieved fine patterning by using a light source of a shorter wavelength and by appropriately selecting a resist composition according thereto.
When a finer patterning is conducted (i.e. making a pattern width smaller) by using the same light source and a photoresist film having the same thickness as conventional patterning, the aspect ratio of a photoresist pattern after development is larger, resulting in pattern collapse. Thus, the photoresist film has been made thinner in accordance with finer patterning to put the aspect ratio of the photoresist pattern within a proper range. Unfortunately, introduction of a thinner photoresist film caused additional technical problem that a precision of a pattern transferring to a substrate to be processed becomes lower.
One of the methods for solving these problems is multilayer resist method. In this method, an underlayer film whose etching selectivity is different from a photoresist film, i.e. a resist upper layer film, is interposed between the resist upper layer film and a substrate to be processed, then a pattern is formed on the resist upper layer film, then the pattern is transferred to the underlayer film by etching using the upper layer resist pattern as an etching mask, and the pattern is transferred to the substrate to be processed by etching using the underlayer film as an etching mask.
In recent years, a silicon-containing resist underlayer film has been used as a resist underlayer film in multilayer resist method (Patent Document 1). The silicon-containing resist underlayer film is excellent in processing performance due to its easy coating property and etching selectivity that is different from an upper layer resist. However, in a composition for forming a silicon-containing resist underlayer film, which is different from a silicon-free organic film composition such as a conventional photoresist composition, once the composition for forming a silicon-containing resist underlayer film begins condensation of a polymer and becomes a higher molecular weight polymer in a pipe or a filter, a solvent-insoluble deposit will be generated. This is derived from a silicon-containing polymer contained in the composition for forming a silicon-containing resist underlayer film. The deposit of the polymer is generally called “siloxane gel”, and its size is significantly small. Therefore the deposit can readily pass through even a filter (approximately 20 nm in diameter) connected to a discharge pipe of a coating apparatus for forming a silicon-containing film, and the deposit is observed as a defect in a silicon-containing coating film formed on a substrate for producing a semiconductor apparatus.
A defect in a coating film is found in the form of minute unevenness generated when a resist composition is applied on a substrate for producing a semiconductor apparatus. A defect contained in a resist film, particularly in a silicon-containing resist underlayer film affects a pattern of a resist upper layer film, frequently leading to a pattern defect. When the pattern defect is transferred to a substrate to be processed for a semiconductor apparatus by dry etching, a circuit in the semiconductor apparatus produced shows electrical faults such as open abnormality and short abnormality. In fact, the pattern defect is a cause of declining yield of semiconductor apparatuses. A currently used method for effectively removing the siloxane gel generated in a pipe or a filter is only filtration by using a filter. Since a filter cannot sufficiently remove a particularly small defect, more effective means is being required.